The shoulder joint is a complex joint with the scapula, clavicle and the humerus all coming together to enable a wide range of movement, at least in a properly functioning joint. In a properly functioning shoulder joint the head of the humerus fits into a shallow socket in the scapula, typically referred to as the glenoid. Articulation of the shoulder joint involves movement of the humeral head in the glenoid, with the structure of the mating surfaces and surrounding tissues providing a wide range of motion.
The shoulder joint can undergo degenerative changes caused by various issues, such as rheumatoid arthritis, osteoarthritis, rotator cuff arthroplasty, vascular necrosis or bone fracture. When severe joint damage occurs and no other means of treatment is found to be effective, a total, partial, or reverse shoulder replacement or reconstruction may be necessary. Total shoulder replacements can involve a humeral prosthetic, including a stem and a head portion used to replace the natural humeral head. Total shoulder replacements will also typically involve resurfacing of the glenoid with a prosthetic implant. The glenoid implant generally will include an articulating cup shaped to receive the prosthetic humeral head. A reversal shoulder replacement (arthroplasty) involves a different set of humeral and glenoid replacement prosthetics. In a reverse shoulder the humeral component includes a cup shaped articular surface attached to a stem implanted into the humerus, while a spherical glenoid component is used to provide an articular surface for the humeral cup.
During shoulder arthroplasty surgery, the components of the prosthesis are matched with the bio-kinematics of the patient in an effort to maintain or restore a natural range of motion of a healthy shoulder joint. Patient specific instrumentation, such as Zimmer PSI (add reference), can assist a surgeon in planning and implementing a shoulder arthroplasty to restore natural bio-kinematics. However, even with the multitude of advances in prosthetic components and patient specific instrumentation, restoring a full range of motion can remain difficult, especially for a surgeon who does not regularly perform shoulder replacements.
Even current surgical standards are often vague, providing guidance such as joint tension should be 50/50 laxity or the joint should be “stable” throughout the range of motion. It is common for the current surgical standards to use un-quantified subject measures, such as if the fit is “too tight” perform any necessary soft tissue releases. Without significant experience, such guidance is of little practical use in ensuring successful outcomes.
While the above discusses issues and procedures specific to shoulder replacement procedures, discussion of the following systems, devices, methods, and instruments is also applicable for use in other joint replacement procedures, such as total hip arthroplasty (THA) or total knee arthroplasty (TKA).